This invention relates to the forming of concrete slabs in situ for protecting earthen, and particularly sloping earthen, surfaces against erosion by virtue of flexible fabric forms. A plurality of novel connectors are used in conjunction with overlying sheets of flexible fabric to provide a form which readily comports to the surface on which it rests and yet insures that when a cementitious slurry is introduced between the overlying sheets a resulting slab of substantially uniform thickness is produced.
In order to control erosion along earth embankments, hill slopes and shorelines, concrete slabs and structures are placed, or constructed, at such sites. Construction along a sloping, undulating terrain is made possible by the use of flexible fabric, or bag-like, forms which allow the structure to conform to the underlying surface contour of the earth, while preventing the cementitious slurry from slumping under the influence of gravity before hardening.
The fabric bags, or sheets, are placed on the site at the desired, permanent location for the finished structure. A cementitious slurry is pumped into the bag-like form where it hardens into the concrete structure. In order to prevent unregulated flowing and bulging of the slurry within the fabric sheets themselves, and to control the thickness of the concrete layer to be formed, it is necessary that means to fasten and means to space the upper and lower layers of fabric sheets be employed at regular intervals.
A variety of fastening and spacing means are known to the art, each having its own drawbacks. In one prior art embodiment the two layers of fabric are stitched, or sewn, together at regular intervals to reduce the excessive bulging of the flexible form at lower levels of the slope which results if the slurry is permitted to slump before hardening. But the thickness of the structure formed is not even substantially uniform -- there is little or no concrete deposited in the area covered by, and immediately surrounding, the stitching. In addition, stitching or sewing at the construction site often is not feasible, so that the fabric must be sewn and prepared beforehand, without regard to the peculiarities of specific sites.
In another prior art embodiment, fastening is accomplished by pulling both overlying layers of fabric through a ring and preventing retraction by use of a pin, spike or other stop means. As with stitching, the structure formed lacks substantially uniform thickness -- no concrete being present at the point of juncture. Although the fabric can now be prepared on site, the preparation involves the tedious, inefficient process of grabbing both layers of fabric, drawing them through the ring, and fastening them there.
In yet another prior art embodiment, a plurality of threaded rods are anchored in the ground, and one or more stop means are received on each rod to serve as the elements by which to control the extent to which the overlying sheets separate when slurry is introduced therebetween. With this arrangement it is generally necessary to prepare the fabric beforehand with holes for the rods, so that the fabric is not torn during installation. The expense of the rods and stop means is a factor that must be considered, as well as the tedious labor of fastening the stop means to the rod after insertion through the fabric at the construction site.
Another type of fastening means employed with flexible, overlying sheets comprises a network of thick cords, attached to one sheet of fabric by stitching or wire hooks, and either interwoven with corresponding cords from the other sheet of fabric, or clipped by a wire hook to such cords. Here, too, the fabric must be prepared before installation at the site, with the attendant expense of pre-preparation.
Wire hooks are sometimes sewn onto one layer of fabric before transporting to the construction site. The second layer is then hooked onto the wire on site. In addition to the expense of using multiple component fastening means -- i.e., the wire hooks and the stitching -- the drawbacks common to all methods which require preliminary preparation of the fabric also exist.
The optimal means for fastening and spacing the fabric in this art should be: inexpensive; capable of being installed quickly and easily on site; capable of imparting substantially uniform thickness to the structure when inserted at approximately 6 to 24 inch intervals; and, should be able to withstand on the order of an eighty pound tensile load, when so spaced, for every two-inch thickness of concrete desired.